Serial Links Rev Up to 56 Gbit/s

SAN JOSE, Calif. — At a meeting in Berlin next week, engineers are expected to submit some of the first public proposals for creating links that carry data at rates up to 56 Gbit/s. The Optical Internetworking Forum's work will lay a foundation for separate efforts to drive Ethernet to 400 Gbit/s now and 1 Terabit/s speeds in the future.

Today's most advanced networks are using 25G serial interfaces now emerging from the lab. A lively debate has sprung up over whether 40 or 50G links will be the next big building block for Ethernet and other network technologies.

"I don't think there's enough material in the public domain to make those decisions yet," said David Stauffer, chairman of the physical and link layer working group at the Optical Internetworking Forum (OIF), a group of communications specialists who chart the course in high performance interfaces. "Some companies have opinions, but there is no industry consensus yet."

The demand for faster data rates is clear. Datacenters and telecom operators have been calling for terabit rates -- something comms engineers say are not yet practical.

Working at the bleeding edge, engineers in Norfolk, Va., also will meet next week to start formal work on a 400GE standard, IEEE 802.3bs. They are expected to hammer out an initial spec based on 16 25G serial lanes

"That's a lot of wires and pins," said Stauffer. "To get to 400G, you really need to get to 50G lanes."

The OIF initially will work on four flavors of 56G. They include a spec that covers half a meter of board traces and one connector, a chip-to-module project, and two very short-reach proposals. Both the very short-reach projects will link serdes and switch chips, one across about 5 cm of board space and another over just a centimeter on an interposer in a 2.5-D chip stack.

"These interposer solutions will become more prevalent to get to the integration levels people need -- switch chips just don&'t have room for all the SerDes they need on board anymore," said Stauffer.

Delivering a 56G backplane specification may require a whole new signaling technology. The widely used nonreturn to zero method will not stretch 56G signals the meter of board space backplanes need, Stauffer said.

The OIF will require all the 56G proposals to work down to 40G speeds. Whether 40 or 50G becomes the new baseline will depend on how much cost and power the technology requires.

"People are looking for the fastest path forward to get faster throughput and still stay in the current power profiles -- power is everything these days," he said.

Stauffer's employer, the startup Kandou Bus, expects to make multiple proposals at the Berlin meeting. But just what concepts get traction at the forum remains to be seen, he said.

Meanwhile, engineers continue to push 25G links to longer reaches. The IEEE 802.3bj spec for backplanes added forward correction to the OIF's 30-inch spec to extend it to 40 inches for backplanes.

"Any of these could go to a cable if the signal loss is consistent with the backplane," Stauffer said. "You might get somewhat longer than a meter on a cable because a cable is more controlled. I am sure there are systems vendors doing that, but they wouldn't have to tell anyone about it."

the OIF has always been the leader in laying down the foundation for all the high speed interconnect signaling, and has a solid track record of getting it right!, by matching need, to the technology which is affordable, and fab ready, the resulting roadmaps from the OIF have then widely implemented. Under the strong leadership of industry experts like David Stauffer, we can be ensured the OIF's track record of 'getting it right' will continue.

It is critical ALL of the industry continue to support these efforts.

The complete Eco-system of suppliers and consumers of this technology 'will be' and 'need to be' at the table to ensure success. We all look forward to the outcome.

For enabling the industries using Terabit interfaces this kind of incremental developments in serial data rate is very much expected and welcomed by the industries. Infect these kind of developments are indeed required to cope up the increasing demand of data access.